This section provides background information related to the present disclosure which is not necessarily prior art. This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Pain is a major limiting factor in many common procedures performed in the inpatient and ambulatory care settings. A very abbreviated list includes skin biopsy, fine needle aspiration biopsy, IV insertion, vaccination, injections (including injection of anesthetics), blood draws, central line placements, and finger and heal pricks for blood analysis (glucose measurement). Pharmacologic anesthesia is a primary method of pain reduction, but the delivery of local pharmacologic anesthesia usually requires a painful injection. Other methods of providing anesthesia include the application of cold temperatures through ice, liquid evaporation, or low temperature substances. These methods of anesthesia are limited in part by the lack of temperature control and the inability to tightly focus the tissue area receiving anesthesia. The present device improves patient comfort by providing tightly controlled, focal cooling to the tissue needing anesthesia or analgesia.
The ocular surface is a tissue surface to which the present device can be applied, but is not limited to. The ability to deliver medication directly into the eye via intravitreal injection therapy (IVT) has transformed the treatment landscape of a number of previously blinding diseases, including macular degeneration and diabetic retinopathy. The success of these therapies in preventing blindness has resulted in a dramatic increase in the number of intravitreal injections performed, with an estimated 4.1 million injections given in the United States alone in 2013. The number of indications for IVT continues to expand, increasing utilization of this therapy significantly every year. The primary limitations of IVT are patient discomfort, ocular surface bleeding, and the time constraints of treating the vast number of patients requiring this therapy. These drawbacks relate to the difficulty of delivering ocular anesthesia to the highly vascularized ocular surface.
To give an ocular injection, the physician first provides ocular surface anesthesia by one of a number of methods, including the following: topical application of anesthetic drops; a subconjunctival injection of lidocaine; placement of cotton tipped applicators soaked in lidocaine above the planned injection site, placement of topical anesthetic gel, or some combination of these. Following ocular anesthesia, the physician or an assistant sterilizes the periocular region by coating it in betadine or a similar antiseptic. An eyelid speculum is then placed, and the physician marks the location of the injection using calipers that guide placement of the needle. The ocular surface is again sterilized, and the physician gives the injection.
Current methods of local anesthesia have unique drawbacks and patients often experience discomfort during and after intraocular injections. The number of indications for IVT continues to expand, increasing utilization of this therapy significantly every year. In light of this need, we have designed a device to deliver rapid anesthesia and vasoconstriction through the cooling of the surface of the tissue at the injection site, which will be discussed in greater detail herein.
Most patients receiving IVT receive multiple injections per year. In 2004, Friedman and colleagues applied age, ethnicity, and gender specific rates of AMD to the 2000 US census and estimated that 1.75 million Americans had exudate macular degeneration. Population based estimates suggest that this number will increase to 2.95 million or more by the year 2020. Using these same principles, Western Europe was estimated to have over 3.3 million patients with exudative macular degeneration in 2004. These numbers are likely underestimates of the true prevalence of disease. The majority of these patients are receiving IVT multiple times per year in one or both eyes. Recent studies have demonstrated that IVT is at least as successful as laser therapy to treat vision threatening retinal disease in patients with diabetic retinopathy and retinal vein occlusions, and this has resulted in wider adoption of IVT in these patients. The number of patients with treatable retinal diseases has increased steadily and will continue to grow over the next several decades. This has led to severe strain on clinic work flow, as IVT is a time-consuming procedure. Vitreoretinal surgeons perform these injections in busy clinics, frequently treating 60 to 70 patients per day. These injections are painful, and ophthalmologists typically choose one of two anesthesia options for IVT. The most common is to provide maximal anesthesia by one of two methods, which increases the time for patient preparation by several fold. The second option is to provide minimal anesthesia via topical drops, which is more time efficient, but results in significant patient pain. Both methods require a technician to prepare each patient. Developing a device to provide rapid anesthesia of the ocular surface will improve patient comfort and physician efficiency.
A recent case report and our own clinical experience show that excellent anesthesia is possible with the application of ice to the ocular surface. This therapy has been used for patients with allergies to lidocaine, but has much broader implications for all patients receiving IVT. Additionally, histopathologic safety data from historic studies of cryotherapy for the treatment of retinal tumors have shown that the operable temperature of the present device will not result in ocular tissue damage. Thus, the present device can improve patient comfort while simultaneously increasing physician efficiency delivering IVT.
Thermoelectric cooling provides reliable refrigeration as well as precise temperature control by direct electric feedback, which is hard to achieve with other available cooling techniques such as liquid evaporation, Joule-Thomson cooling, a thermodynamic cycle (e.g., a Stirling cooler or vapor compression refrigeration cycle), an endothermic reaction, or a low-temperature substance (e.g., liquid nitrogen). However, current thermoelectric (Peltier) modules have a low coefficient of performance (COP) and do not provide sufficient cooling power flux to maintain tissue at a temperature relevant for anesthesia (e.g., −5° C.) if a single unit is placed with its cooling surface in contact with tissue. As specified in the present teachings, the present device adopts a novel cooling power concentrator that collects the cooling power of multiple (or single) Peltier modules and concentrates this cooling over a small area, producing a sufficient cooling power flux required for rapid and sustainable low temperature cooling of tissue. In addition, the cooling power concentrator allows multiple Peltier modules to be distributed over a large area, minimizing the heat flux rejected from Peltier modules to the heat sink and hence relaxing the heat dissipation requirements of the heat sink.
According to the principles of the present teachings, a cryoanesthesia or analgesia device and method of use in ocular treatments is provided that allows for rapid administration of anesthesia to the eye, for example, for administration of intravitreal injections, for example. In some embodiments, by providing cooling of the conjunctiva and sclera at the injection site, patient discomfort is minimized.
In some embodiments, the cryoanesthesia device of the present teachings is designed to achieve a cold temperature quickly by means of a thermoelectric (Peltier) device, liquid evaporation, Joule-Thomson cooling, a thermodynamic cycle (e.g., a Stirling cooler or vapor compression refrigeration cycle), an endothermic reaction, and a low-temperature substance (e.g., liquid nitrogen). The cryoanesthesia device may be sufficiently sized to be handheld or be part of a larger unit, and may include safety mechanisms to limit cooling to a defined temperature, maximum heat flux, or time period in order to prevent damage to ocular or other biological tissue. In some embodiments, the cryoanesthesia device of the present teachings can comprise an applicator attached to a larger cooling unit. The cryoanesthesia device may be a stand-alone, hand-held unit. Use of the cryoanesthesia device of the present teachings improves anesthesia and reduces pre-injection prep time for patients and physicians.
It should be understood, however, that the cryoanesthesia device of the present teachings can be used to decrease pain in any part of the body, including, but not limited to, the cutaneous membranes, mucous membranes, and tissue of the mucocutaneous zone.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.